A lithographic printing plate generally comprises a hydrophobic (lipophilic) image area which repels a fountain solution and receives ink and a hydrophilic non-image-area which receives a fountain solution in printing process. Such a lithographic printing plate is generally produced by mask-exposing a PS plate comprising a hydrophilic support having provided thereon a lipophilic photosensitive resin layer through a lith film and dissolving and removing the photosensitive resin layer of a non-image area with a developing solution.
Digitized techniques of electronically processing, accumulating and outputting image data with a computer have prevailed in recent years, as a result, computer to plate (CTP) techniques capable of directly making an image on a printing plate precursor by scanning highly directional rays such as laser rays in accordance with digitized image data without using a lith film have been developed.
Of such techniques, lithographic printing plate precursors requiring no development which can be used for printing as they are by mounting on a press without development processing after exposure have also been studied for further rationalization of processing and solving the problem of waste solutions. For example, various CTP printing plates requiring no development are described in Bulletin of Printing Institute of Japan, Vol. 36, pp. 148 to 163 (1999).
As one promising method, there is a method of using a heat-sensitive lithographic printing plate precursor having a hydrophilic layer (an image-forming layer) comprising hydrophobic polymer fine particles dispersed in a matrix such as a crosslinked hydrophilic resin and the like. That is, the hydrophobic polymer fine particles are melted and coalesce when heat is applied to the hydrophilic layer, and the heated part of the hydrophilic layer is converted to a hydrophobic image. It is known that a printing plate having the surface consisting of such a hydrophobic image area and a hydrophilic layer part not to be heated (a non-image area) requires no treatment such as liquid development, and can be used as a lithographic printing plate using a fountain solution with no treatment.
It is also known that a heat-sensitive lithographic printing plate precursor using microcapsules encapsulating a hydrophobic substance in place of the hydrophobic polymer fine particles can also be used as a lithographic printing plate using a fountain solution with no treatment. In this case, when heat is applied to the hydrophilic layer, the microcapsules are ruptured and the encapsulated hydrophobic substance oozes out and the hydrophilic layer is converted to a hydrophobic image area.
For instance, heat-sensitive lithographic printing plate precursors comprising a support having provided thereon a hydrophilic layer comprising a matrix obtained by crosslinking a hydrophilic binder, e.g., polyvinyl alcohol, with hydrolyzed tetraalkyl orthosilicate containing thermoplastic polymer fine particles are described in Research Disclosure, No. 33303 (January, 1992), and Japanese Patent 2938397.
Japanese Patent (Application) Laid-Open Nos. 1849/1995, 6468/1998 and 70756/1999 disclose heat-sensitive lithographic printing plate precursors having a hydrophilic layer comprising a crosslinked hydrophilic binder polymer having dispersed therein microcapsules encapsulating a lipophilic component, and the above patents disclose that these heat-sensitive lithographic printing plate precursors can be used for printing with no treatment after the application of heat.
Japanese Patent Laid-Open Nos. 226597/2002 discloses a heat-sensitive lithographic printing plate containing hydrophobic polymer fine particles covered with inorganic fine particles in hydrolyzed tetraalkyl orthosilicate.
However, the hydrophilic property and press life of the hydrophilic layer are insufficient in these conventional techniques, and thereby a problem that the scumming is gradually generated in a non-image area when the printing is continued, arises in these conventional techniques.